A computer readable medium storing a program causing a computer to execute a process for authenticating a user in a site included in an authentication system in which a plurality of sites are linked each other, the process comprising: receiving authentication information; authenticating the user in a first site of the authentication system based on the received authentication information; receiving suspicious behavior information of the user; registering the received suspicious behavior information; determining reliability of the user based on the suspicious behavior information registered in registering of the behavior information registration; in a case where the user accesses a second site of the authentication system, adding the reliability of the user determined, and transmitting the authentication information to which the reliability is added to the second site; and determining a function to be provided to the user in the first site based on the reliability of the user.